1. Field of the Invention
This invention relates to a photomask for exposure to an optical near-field, to a method of controlling an optical near-field intensity distribution using such a photomask, to a pattern preparing method, and also to a pattern preparing apparatus.
2. Related Background Art
With the current advancement of technology brought forth to realize semiconductor memories having a higher memory capacity and CPUs that operate at a very high speed, and show an enhanced degree of integration, photolithography is inevitably required to accommodate micro-processing operations with smaller dimensions. Generally, the dimensional limit of micro-processing of a photolithography apparatus approximately corresponds to the wavelength of the light source to be used for photolithography. Therefore, a near-ultraviolet laser is often used as a light source for a photolithography apparatus in order to reduce the dimensional limit. Thus, currently, photolithography apparatuses are feasible for micro-processing on the order of about 0.1 μm.
While the dimensional limit of micro-processing is reduced for photolithography, there are still a number of problems to be solved for photolithography if it is to be used for micro-processing of 0.1 μm and less. For example, a light source having a shorter wavelength may be needed. Then, lenses that can be used for such a short wavelength may have to be developed.
Near-field exposure methods have been proposed as a possible solution for these problems. For example, U.S. Pat. No. 6,171,730 proposes an exposure method and an exposure apparatus that utilize an elastically deformable mask having a micro-aperture pattern of an opening with a width not greater than 100 nm on the front surface and made of an elastic material so as to be deformable along the normal line relative to the mask surface. The method and the apparatus as disclosed in the above-cited patent document are excellent, and have contributed greatly to the technological field to which the present invention relates.
However, when g-rays having a wavelength of 436 nm or i-rays having a wavelength of 365 nm are used for a micro-aperture pattern with a width not greater than 100 nm, as disclosed in U.S. Pat. No. 6,171,730, the width of the openings is less than one half of the wavelength.
In an operation of near-field exposure using a near-field formed by light by way of a micro-aperture in a metal film, the optical near-field intensity distribution can be different from the contour of the aperture.
Meanwhile, U.S. Pat. No. 6,236,033 proposes a photolithography mask formed having a metal film with an aperture and a surface profile that undulates periodically so as to interact with surface plasmon modes and intensifies the transmission of light through the aperture for the purpose of transferring an image. However, while the above-cited patent proposes to boost light obtained through the aperture, it does not propose to weaken light and make uniform the intensity distribution of light.